EXALTONE.RTM. and muscone, two macrocyclic ketones, are very appreciated in the art for their elegant and tenacious musky odour. Both compounds have been known for several decades and since their discovery, a variety of syntheses have been proposed and described in the scientific literature [see e.g. J. Chem. Soc. 1964, 4154; Tetrahedron 20, 2601 (1964); Helv. Chim. Acta 50, 705 (1967) and Helv. Chim. Acta 50, 708 (1967)]. So far however, most of the published methods could not be sucessfully applied to their industrial scale preparation, especially in view of their complexity or in view of the low yields achieved in the critical reaction steps.
One of the prior known syntheses [Helv. Chim. Acta 50, 705 (1967)] is making use of the bicyclic hydrocarbon of formula ##STR6## as intermediate in the synthesis of EXALTONE.RTM. (cyclopentadecanone), and of the corresponding methyl derivative of formula ##STR7## in the synthesis of muscone. Both intermediate compounds can be obtained from cyclododecanone, by a condensation reaction and a subsequent cyclization, hydrogenation and dehydrogenation. Due to rather poor overall yields however, such synthetic routes do not present any major interest to the industry.
The afore mentioned bicyclic hydrocarbons can in fact be prepared in a more rational and more advantageous manner, by reacting the above compounds of formula (VI) with an isomerizing agent such as a strong material or organic acid e.g.